Recent Doppler ultrasound technological advances have demonstrated the unique capability to detect microemboli in the arterial and venous circulation. Microemboli have been implicated as the source or prelude of stroke and associated neurologic deficit. An unknown that would help determine the underlying pathology and the appropriate therapy is the composition of the individual microemboli. This proposal is to adapt advances in ultrasound echo processing, transducer, and harmonic detection technologies to determine microembolus composition as bubble or solid (formed element). Three areas of development are set forth: (1) adapting an existing digital Doppler platform to perform second harmonic Doppler analysis of echoes from microemboli, (2) developing a wide bandwidth ultrasound probe for normal Doppler processing at 1 MHz and second harmonic Doppler processing at 2 MHz, which have similar sensitivity patterns for each frequency, and (3) determine in vitro the best detection scheme for maximizing the ability to distinguish microbubbles from microparticles. This technology is especially important for reducing the incidence of stroke and neurologic compromise associated with various cardiovascular pathologies and surgery of the heart and of the carotid arteries. A device for discrimination of composition of microemboli represents a major commercial market potential. PROPOSED COMMERCIAL APPLICATIONS: The instrument to be developed in this project will characterize microemboli in blood flow as either gaseous or particulate, using ultrasound first and second harmonic Doppler analysis of microembolic signatures. This instrument will not require a user who is an ultrasound expert, and will target physician and technologist staff in the operating room, vascular laboratory, and emergency medicine markets. This simple to use ultrasound device will be aimed at a worldwide market.